The broad long-term objective of the proposed research is to better understand mechanisms controlling skeletal muscle hypertrophy in elderly men. This is relevant to elderly men as sarcopenia or the age related loss of skeletal muscle mass is highly prevalent in this population. Specifically we will be examining the effects of altered circulating testosterone concentrations, resistance training, and the combination of these two interventions on skeletal muscle hypertrophy and putatative mediators of skeletal muscle hypertrophy: insulin like growth factor I mRNA, insulin like growth factor I protein, and satellite cell activation (skeletal muscle concentrations of MyoD and myogenin). We will alter testosterone concentrations with megestrol acetate and testosterone administration and will induce skeletal muscle hypertrophy with resistance training in the following experimental design: 1) A non-intervention control group; 2) megestrol acetate administration; 3) megestrol acetate administration + resistance training; 4) megestrol acetate administration + 100 mg of testosterone enanthate per week; 5) megestrol acetate administration + resistance training + 100 mg of testosterone enanthate per week.